1. Field of the Invention
This invention relates to solar energy technology and, in particular, to the testing of materials and articles for resistance to solar light and weather factors with the use of concentrated solar radiation.
2. Description of the Prior Art
The combined action of atmosphere and solar radiation causes irreversible changes (degradation and natural aging) in various materials and articles. The most typical and important (with respect to technical and economic factors) examples of such changes are manifested as changes in the color of construction and finishing of materials, paints and varnishes, textile dyes (known as fading or discoloration), and degradation of mechanical characteristics of polymeric materials which can be demonstrated as the effect of embrittlement and destruction of polyethylene films used in hothouses after only one or two seasons.
The rate of these and other degradation processes depends on the composition of the atmosphere, temperature, and exposition to light. The exposition to light irradiation is most pronounced in the ultraviolet (UV) region of solar spectrum (290-450 nm). The physical nature of the predominant effect of UV radiation of the Sun in material degradation processes is caused by the fact that the energy of photons of solar light in this part of spectrum corresponds to the energies of rupture of typical chemical bonds of organic and organoelement compounds (C--C; CN; C--O; C--F; C--Cl, etc.).
Irradiation of materials with the light of the long-wave (visible and infrared) regions of solar spectrum is responsible only for the heating of materials.
The above mentioned dependence of irreversible changes in coloration of coatings and materials on the exposition to sunlight is the critical factor with regard to long-run behavior of facade coatings and panels of buildings under different complex conditions of illumination inside city districts. Therefore, testing and certification of different materials and articles which are sensitive to irradiation with natural sunlight is of great practical and economic importance.
At present, the simulation of irradiation conditions, particularly the simulation of multiple concentrations of radiation in combination with a set of different atmospheric factors which affect the samples, represents a complex technical problem. This is caused by a series of physical and technical factors as follows: the spectrum of even the best specially developed metal-halogen lamps simulating natural sunlight radiation shows the pronounced linear structure, particularly in UV spectral range of interest; hence, it should be expected, that mechanisms of material degradation induced by natural sunlight, and the light of the said lamps may differ significantly; the uniformity of irradiating flux density over an entire target area should be very high (within several per cent) in order to provide good reliability of testing measurements; and to decrease the factor of excessive heating of samples under test due to absorption of visible and infrared portion of solar light it is necessary to provide special measures (in addition to possible cooling of samples), in particular, to filter off visible and infrared portion of solar radiation from a flux incident onto samples.
In the prior art, a series of concentrators have been disclosed which represent the parts of solar setups for accelerated sunlight weathering tests and using concentrated solar radiation. For example, the solar setup in USSR Inventor's Certificate 139513, IPC GO1H 17/02 discloses equipment which is intended for testing materials and includes a concentrator consisting of six flat mirrors, each 2.times.1.3 m in size. These mirrors are installed in pairs on three mechanically interconnected platforms. The platforms move together and one after another along two rails put on a circle path 7 m in radius. The flat unit, 2.times.1.3 in size, with the samples under test is located in the center of this circular path. However, high materials consumption and, consequently, large weight, complex kinematics of the Sun tracking, and impossibility to attain high concentration ratios (of the order of 100) of solar radiation are obvious disadvantages of this design.
In USSR Inventor's Certificate 1746157, IPC F24J 2/42, a parabolic trough concentrator is disclosed which is a part of solar setup described. This concentrator is composed of flat facets. However, the design of this concentrator is also characterized by complex Sun tracking and impossibility of obtaining high solar concentration ratios.
In USSR Inventor's Certificate 1800243, IPC F24J 2/42 a prototype concentrator design is disclosed which is composed of flat facets. The design of this concentrator has an important disadvantage in that an increase in concentration ratio can be achieved also only by application of complicated kinematics of rotating samples in a target plane.
In view of the foregoing, what is needed is an improved apparatus and technique which provides performance of accelerated testing, but which simulates the duration of the processes leading to the degradation in the main characteristics of materials (chromatic, mechanical, and others) and consequent loss of trade quality which occurs from several months to several years.
Additional advantages of the present invention will be set forth in part in the description that follows and in part will be obvious from the description or can be learned from practice of the invention. The advantages of the invention can be realized and obtained by the method particularly pointed out in the appended claims.